servos are way better.they don't lose tourque with speed,they don't resonate like steppers and they are faster.high quality steppers are OK,but servos are even better and low quality steppers are bad.the servos also know where they are which could be benefial in some applications.
if money is not the object go with servos.if money is the object then go with steppers.you can get 4 stepper motors and a controller cheaper than one servo with controller and power supply.